Self-extinguishing cellulose acetate molding compositions



Patented Nov. 18, I952 SEEF-EXTINGUISHING CELLULOSE ACE- TATE MOLDING COMPOSITIONS Lester Wl- A. Meyer and William M. Gearhart, Kingsport; Tenn., assignors to Eastman Kodak" Company, Rochester, N. Y., a corporation of New Jersey Nonmwing; Application September 16,1949,- Serial No. 116,204

Cellulose acetatecompositions plastioized with the usual cellulose acetate plasticizers; such,-- for instance; as'the lower al-k-yl-phthala-tes; are notsuitable for many applications vvhich require ahigh degree offlame resistan'cer Ti iphenylpho's phate in high proportions has be'en used as aflame+proofing agent} but,althoughit reducesthe fia'mmability somewhat, the resulting compositions are not self extinguishing. Moreover,- the triph'enyl phosphate exudesreadilyin softer-flows of-the plastic; Fromtime totimevarious fillers,

sueh forinstance, as antimony oxide,-have beenproposedas flame-proofingagents in cellulose acetate plastics; but-none has proved verysuccessful; It has-been known that-tri-monoohloroethyl phosphate plasticizes and reduces-th'e'flamm'ability of cellulose acetate, but it has nothitherto been possible to moldcellulose acetate compositions: containing tri-monochloroethyl phosphate;

Tri-monochloroethyl phosphate has a high degree ofsolvent powerior celluloseacetate; anda" mixture of the two substances will readily mill However, if the tri -monoint'o a: clear sheet. chloroethyl phosphate is used as'the sole plas ticizer with cellulose acet'atain the amounts in which plasticizers areusually used to obtain the commercial flow range (25 to 50 parts of plasticizer per 100 parts" of cellulose acetate by weight), theresulting plastics: are found to be somewhat too brittle for injectionniolding- This brittleness can be appreciably diminished by the addition of other plasticizers, but care must be taken that the excellent flame-proofing properties of the tri-monochloroethyl phosphate? are not diminished by the' other plasticizer. Most useful plasticizersin this" respect are other phosphates; such as triphenyl phosphate, tric're's'yl phosphate, and tributyl phosphate, which in themselves have some flame-proofing qualities. Other known plasticizers, such, for instance, as the dialkyl phthalates, the sulfonamides, and the ethoxyethyl esters of adipic and sebacic acids, may be used, but it is then necessary to use larger quantities of tri-monochloroethyl phosphate than when another phosphate is used as co-plasticizer.

The problem of stabilizing the tri-monochloroethyl phosphate without sacrificing the desired qualities or the plastic is more difi'icult; Ti-imonochloroethyl phosphate is not as inherently stableto heat at molding temperatures asarethe commonly used plasticizers. This instability to; heat results'inhydrochloric'acid being givenoif from the tIleI'l'iOIlOChlOIOBthYl phosphate and; in" turn breaking down the cellulose acetate? The breakdown products render the'plastic'unus'able in any commercial molding or extrusion process; as the hydrochloric acid rapidly corrodes the mold. In addition, the odorfrorrr the'breaking-'" down plastic is very objectionable to the operators of the molding machine.

Large amounts of stabilizing salts; such as antimony oxide or magnesiun'i'carbonate;v can be used successfully to stabilize celluloseacetate compositions containing" trimonochloroethyl phosphate, but they render the plastic a dense,

White material, whichv greatly restricts its" use. For some purposes,- such, for instance; as the manufacture of speciallyishaped and colored-light" bulbs for ornamental purposes, it is desirable to have a highly translucent plastic, which can be molded, particularly by theinjection molding. process; and which is self-extinguishing: if. i'g -i nited. Such light bulbs and similar ornamental objects are commonly used in close proximity to highly inflammable" material, such as paper,

cloth, and evergreen branches, and'it--is highly important that the plastic shouldnot contribute further flammability to the decorative ensemble.

We have discovered thatv a completely selfextinguishing, highly translucent cellulose acetate plastic; which can be injection" mol d or dry-extruded without discoloration or physical breakdown, and'which does not exude'plasticia'er" under extreme conditions of heat and'humidity, can be compounded by plasticizing parts'of cellulose acetate with from. 20"to"70parts' of a mixture of plasticizers 'Which'incluclesfrom '17 to 50 parts of tri-monochloroethyl phosphate per 100 parts of cellulose acetate and incorporating in th composition approximately? to 5 parts; preferably 3 parts, of lead maleate 'pe'r100" parts of cellulose acetate. Lead maleat'e'isuniqii as a stabilizer for such compositions in tlia'tsuch a small amount of it is required that the plastic is highly translucent. Two parts of lead maleate give a plastic which approaches borderline stability. Five parts gives as much stability as can be expected from this stabilizer,'and additional amounts would serve no useful purpose. A plastic containing 5 parts of lead maleate per 100 parts of cellulose aceate is too dense for many applications, but can be used in some cases to 3 insure maximum stability. The optimum concentration is 3 parts lead maleate per 100 parts of cellulose acetate for stability and maximum translucency.

The lead maleate Which We prefer to use as a stabilizer is the so-called normal salt, in which one atom of lead is combined with maleic anhydride according to the formula It is possible to combine 2 and 3 atoms of lead with maleic anhydride. We have tested these forms and found that they will function as stabilizers but impart higher density. The 3-atom combination also tends to give a yellow color to the plastic.

Flame resistance of the plastics is determined by A. S. T. M. Method D635-44, described in A. S. T. M. Standards, 1944, Part 3, page 527. The stability Or resistance to breakdown on heating is measured by A. S. T. M. Method D569-48, described in A. S. T. M. Standards, 1948 Supplement, Part 313, page 13. In this test the plastic is heated for one hour at 205 C. The flow should not break down more than one or two flows.

As examples of our novel compositions, we give the following formulas:

Example I 100 parts cellulose acetate 17 parts tri-monochloroethyl phosphate 20 parts triphenyl phosphate 5 parts diethyl phthalate 3 parts lead maleate This formulation gives a flow of H by A, S. T. M. tests. It is completely self-extinguishing, and can be made up in a variety of colors, by adding the dyes commonly used in cellulose acetate molding compositions. These formulations will go through the injection molding machine or dry extrusion equipment without discoloration or physical breakdown.

Example II 100 parts cellulose acetate 35 parts tri-monochloroethyl phosphate 3 parts dibutyl phthalate 3 parts lead maleate This composition has even greater flame resistance than that of Example I. It is more brittle than the composition of Example I, but it can be successfully injection molded.

These compositions have withstood conditions of 100 F. and 80% relative humidity for one month without exudation of plasticizer.

Example III 100 parts cellulose acetate 20 parts tri-monochloroethyl phosphate 20 parts triphenyl phosphate 3 parts lead maleate 4 Example IV 100 parts cellulose acetate 20 parts tri-monochloroethyl phosphate 20 parts ethyl diphenyl phosphate 3 parts lead maleate Example V 100 parts cellulose acetate 25 parts tri-monochloroethyl phosphate 15 parts tricresyl phosphate 5 parts 0- and p-toluene sulfonamides 3 parts lead maleate Example VI 100 parts cellulose acetate 25 parts tri-monochloroethyl phosphate 15 parts methyl benzy1 phthalate 3 parts lead maleate All parts in the specification and claims are by weight.

What we claim as our invention and desire to be secured by Letters Patent of the United States 1. A cellulose acetate composition which is translucent, self-extinguishing when ignited, and suiiiciently stable at high temperatures to permit of being molded without decomposition of any of the components, comprising 100 parts by weight of cellulose acetate, from 20 to parts of a mixture of plasticizers which includes from 17 to 50 parts of trimonochloroethyl phosphate, no plasticizer more flammable than cellulose acetate being present, and 3 parts of normal lead maleate.

2. A cellulose acetate composition which is translucent, self-extinguishing when ignited, and sufficiently stable at high temperatures to permit of being molded without decomposition of any of the components, comprising parts by weight of cellulose acetate, 17 parts of tri-monochloroethyl phosphate, 20 parts of triphenyl phosphate, 5 parts of diethyl phthalate, and 3 parts of normal lead maleate.

3. A cellulose acetate composition which is translucent, self-extinguishing when ignited, and sufficiently stable at high temperature to permit of being molded without decomposition of any of the components, comprising 100 parts by weight of cellulose acetate, 35 parts of tri-monochloroethyl phosphate, 3 parts of dibutyl phthalate, and 3 parts of normal lead maleate.

LESTER W. A. MEYER. WILLIAM M. GEARI-IART.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,884,433 Vlebb Oct. 25, 1932 1,927,143 Walsh Sept. 19, 1933 2,328,269 Gloor Aug. 31, 1943 2,330,254 Whitehead Sept. 28, 1943 2,397,320 Kock Mar. 26, 1946 

1. A CELLULOSE ACETATE COMPOSITION WHICH IS TRANSLUCENT, SELF-EXTINGUISHING WHEN IGNITED, AND SUFFICIENTLY STABLE AT HIGH TEMPERATURES TO PERMIT OF BEING MOLDED WITHOUT DECOMPOSITION OF ANY OF THE COMPONENTS, COMPRISING 100 PARTS BY WEIGHT OF CELLULOSE ACETATE, FROM 20 TO 70 PARTS OF A MIXTURE A PLASTICIZERS WHICH INCLUDES FROM 17 TO 50 PARTS OF TRIMONOCHLOROETHYL PHOSPHATE, NO PLASTICIZER MORE FLAMMABLE THAN CELLULOSE ACETATE BEING PRESENT, AND 3 PARTS OF NORMAL LEAD MALEATE. 